The invention relates generally to a nasal mask and to a cushion therefor, for example, for use in the treatment of respiratory conditions and in assisted respiration.
Nasal masks are commonly used in the treatment of respiratory conditions and sleep disorders (e.g., obstructive sleep apnea) by delivering a flow of breathable gas for, or to assist patient respiration. These nasal masks typically receive a gas supply line which delivers gas into a chamber formed by walls of the mask. The walls usually are semi-rigid and have a face contacting portion including an aperture which is aligned with the wearer""s nostrils. The face contacting portion can comprise a soft, resilient elastomeric material which may conform to various facial contours. The mask normally is secured to the wearer""s head by straps. The straps are adjusted to pull the mask against the face with sufficient force to achieve a gas tight seal between the mask and the wearer""s face. Gas is thus delivered to the mask and through the aperture to the wearer""s nasal passages.
Problems often arise with masks of the above configuration. For example, the mask may be dislodged, thereby breaking the seal between the mask and wearer. This may occur if the wearer rolls over when sleeping thereby creating a drag force on the gas supply line which is transmitted to the mask, breaking the seal. In the case of a mask being used for the administration of Continuous Positive Airway Pressure (CPAP) treatment for the condition obstructive sleep apnea, such a leak can result in the pressure supplied to the entrance of the wearer""s airway being below the therapeutic value, and the treatment becoming ineffective.
Another problem is that the face contacting portion may apply excessive pressure to the wearer""s face resulting in discomfort and possibly skin irritation. This excessive forces. In some cases these excessive pressures and forces may cause the face to distort to conform with the face contacting portion to increase wearer discomfort, facial soreness and ulceration.
Other types of devices exist whereby small nostril nosepieces (pillows) are held in place by a harness strapped over the wearer""s head, for example as shown in prior art U.S. Pat. No. 4,782,832. While this arrangement may alleviate some problems regarding seal breakage and skin abrasion, the harnesses associated with such devices are quite cumbersome for the wearer, as are the gas supply lines. Also, air xe2x80x98jettingxe2x80x99 into the nostrils can be irritating to the patient making such devices generally uncomfortable to use.
In FIGS. 1-3, a prior art nasal cushion 10, generally equivalent to that shown in prior art U.S. Pat. No. 5,243,971, is first described.
As shown, the cushion 10 generally includes a base 11 from which depends a semi-rigid cushion frame 12 formed of elastomeric material. Attached over the outside of the frame 12 is a membrane 15, also of elastomeric material, having at its distal end a face contacting portion 14. The frame 12 and the membrane 15 generally form a chamber 17 into which the wearer""s nose can be received. The frame 12 has a notch 19 to accommodate the bridge of the wearer""s nose. The base 11 includes slots 13 to accommodate straps (not shown) to secure the cushion 10 and a mask body (not shown) in combination to the wearer""s head.
An aperture 16 is formed at the end of the membrane 15 distal from the frame 12 providing access for a wearer""s nose 20 to the chamber 17 as noted. As shown, the aperture 16 in an unflexed state is generally circular (or elliptical) and is large enough to allow partial entry of the wearer""s nose. The resilience of the membrane material allows the face contacting portion 14 and the aperture 16 to invert when the nose is received. The inverted membrane arrangement relies upon a positive pressure of supplied gas within the mask to effect a seal to the wearer""s face. The seal is characterised as a xe2x80x9crolling edge sealxe2x80x9d, in that there can be motion of the cushion 10 relative to the patient""s face yet the seal is maintained. Even so, a tuck 22 arises in the vicinity of the upper lip due to the circular shape of the aperture, and it is from this tuck that leaks can arise due to head and body movement during sleep.
It is an object of the invention to overcome or at least substantially ameliorate one or more of the foregoing disadvantages.
In one broad form, the invention discloses a nasal mask cushion to sealingly connect a mask to a wearer""s face, the cushion comprising:
a substantially triangularly-shaped frame of resilient material having a rim to surround the wearer""s nose;
a membrane also of resilient material, the membrane being relatively more flexible than the frame, and being of the same general shape as said rim and fixed to and extending away from the frame so as to have an outer surface spaced from the rim, a portion of said outer surface forming a face contacting seal; and
a nose-receiving cavity bounded by said frame and said membrane;
and wherein said seal portion is generally coterminous with respect to said rim and is resiliently deformable towards the rim in use of the cushion.
Preferably, the rim and seal portion are shaped to generally match facial contours of the facial tissue around the sides and over the bridge of the nose and between the base of the nose and the top lip.
In one particularly advantageous form, the membrane is substantially saddle-shaped. The membrane further has a centrally located aperture through which the wearer""s nose passes to enter said cavity.
It is preferred that the cushion and membrane each include a colocated notch to accommodate the bridge of the nose of the wearer. Typically, the seal portion contacts at least the wearer""s nose, and preferably, also the facial tissue around the sides and over the bridge of the nose and between the base of the nose and the top lip.
The invention further discloses a nasal mask for connection to a wearer""s face comprising:
a mask body for connection with a supply of breathable gas; and
a nasal cushion, the body and cushion defining a nose-receiving cavity, the cushion including:
a substantially triangularly-shaped frame of resilient material having a rim to surround the wearer""s nose;
a membrane also of resilient material, the membrane being relatively more flexible than the frame, and being of the same general shape as said rim and fixed to and extending away from the frame so as to have an outer surface spaced from the frame, a portion of said outer surface forming a face contacting seal;
and wherein said seal portion is generally coterminous with respect to said rim and is resiliently deformable towards the rim in use of the mask.
The mask body can further include attachment points from which securing straps can be attached, and by which the mask can be secured to the wearer""s head. The nasal mask can yet further comprise an arm depending from said body from which a further securing strap(s) can be attached.
The invention further discloses nasal CPAP treatment apparatus comprising a flow generator for the supply of gas at a pressure elevated above atmospheric pressure to a gas delivery conduit, the conduit in turn coupled to a nasal mask as described immediately above.
In one particularly preferred form, a supply of gas can be provided to said cavity, said supply of gas assisting, but not solely causing maintenance of a seal by said seal forming portion of said membrane to the face of the wearer in use of the cushion.
Advantageously, because the membrane and the rim are substantially shaped to the facial contour, and the membrane does not need to turn in on itself, as in the prior art, thus contacting the face without folds or creases. With the cushion/mask secured to the wearer""s head, the headstraps need only to be tensioned to balance the force due to mask gas pressure that tends to lift the mask off the face. Such relatively lower mask-to-face pressure results in greater patient comfort, and a reduction in the likelihood of skin irritation.